Polarization and dynamic phases of aligning active matter in periodic obstacle arrays

TL;DR

This study uses numerical simulations to explore how self-propelled particles with alignment interactions behave in periodic obstacle arrays, revealing various polarization phases influenced by obstacle density and anisotropy.

Contribution

It introduces a detailed analysis of polarization transitions and lane formations in active matter within structured obstacle environments, highlighting the effects of obstacle arrangement and anisotropy.

Findings

Polarization transitions occur at critical alignment parameters.

Obstacle arrays can lock polarization to substrate symmetry.

Anisotropic obstacles lead to lane formation and complex polarization patterns.

Abstract

We numerically examine a system of monodisperse self-propelled particles interacting with each other via simple steric forces and aligning torques moving through a periodic array of obstacles. Without obstacles, this system shows a transition to a polarized or aligned state for critical alignment parameters. In the presence of obstacles, there is still a polarization transition, but for dense enough arrays, the polarization is locked to the symmetry directions of the substrate. When the obstacle array is made anisotropic, at low densities the particles can form a quasi-isotropic state where the system can be polarized in any of the dominant symmetry directions. For intermediate anisotropy, the particles self-organize into a coherent lane state with one-dimensional polarization. In this phase, a small number of highly packed lanes are adjacent to less dense lanes that have the same polarization, but lanes further away can have the opposite polarization, so that global polarization is lost. For the highest anisotropy, hopping between lanes is suppressed, and the system forms uniformly dense uncoupled but polarized lanes.